feat(module:tabs): support for start and end extra content

[HyperLife1119]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/NG-ZORRO/ng-zorro-antd/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Application (the showcase website) / infrastructure changes
• Other... Please describe:

What is the current behavior?

Issue Number: N/A

Only extra content at the end is supported.

What is the new behavior?

<nz-tabset [(nzSelectedIndex)]="selectedIndex">
  <button *nzTabBarExtraContent="'start'">Start Extra Action</button>
  <button *nzTabBarExtraContent="'end'">End Extra Action</button>

  <nz-tab nzTitle="Tab 0">Content of Tab Pane 0</nz-tab>
  <nz-tab nzTitle="Tab 1">Content of Tab Pane 1</nz-tab>
  <nz-tab nzTitle="Tab 2">Content of Tab Pane 2</nz-tab>
</nz-tabset>

Supports extra content at the start and end.

Does this PR introduce a breaking change?

• Yes
• No

Other information

[zorro-bot]

This preview will be available after the AzureCI is passed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.01%. Comparing base (1c1c3e4) to head (e4a7396).
Report is 7 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #9097   +/-   ##
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  Coverage   92.01%   92.01%           
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  Files         564      565    +1     
  Lines       20026    20034    +8     
  Branches     3107     3107           
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+ Hits        18426    18435    +9     
  Misses       1261     1261           
+ Partials      339      338    -1     

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[HyperLife1119]

nz-tabset 上也有一个属性为 nzTabBarExtraContent，因此需要排除一下。

我在想是否应该弃用 nz-tabset 上的 nzTabBarExtraContent 用法，引导用户采用现在这种更通用的用法？

[Copilot]

Pull Request Overview

This PR introduces support for rendering extra content at both the start and end of the tabset. Key changes include:

• Adding a new binding ([extraContents]) and helper (contentChildren) in the tabset component.
• Updating the tab navigation bar to render start and end extra content using Angular 17’s computed and input signals.
• Updating tests, docs, and demos to reflect the enhanced functionality.

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
components/tabs/tabset.component.ts	Added support for extra content binding and integrated extraContents.
components/tabs/tabset.component.spec.ts	Added tests to verify rendering of start and end extra content.
components/tabs/tabs.module.ts	Updated module exports to include the new extra content directive.
components/tabs/tab-nav-bar.component.ts	Implemented computed signals to conditionally render extra content.
components/tabs/tab-bar-extra-content.directive.ts	Created new directive for specifying extra content position.
Documentation and demo files	Updated to demonstrate the new functionality.

[Laffery]

LGTM